1. Field of the Invention
The present invention relates to a vibration damping mechanism and an anti-earthquake wall material for reducing the vibration of a structure such as a building.
2. Description of the Prior Art
A vibration damping mechanism which uses a viscoelastic body to efficiently reduce the vibration of a structure has been given in Japanese Unexamined Patent Publication No. 7 (1995)-247727. According to this patent publication, there is disclosed a vibration damping mechanism in which a first pivot and a second pivot are mounted to opposed frame members of a structure, respectively, with an appropriate spacing, a first fixed plate which is rotatable with respect to the first pivot, and a second fixed plate which is rotatable with respect to the second pivot are opposed with a gap between them, and a viscoelastic body is filled into this gap, and with this vibration damping mechanism, the viscoelastic body is selected according to the conversion factor .beta.=L/h.
With the conventional vibration damping mechanism, the viscoelastic body is selected according to the conversion factor .beta.=L/h, which makes it difficult to manufacture the vibration damping mechanism. In addition, the vibration damping mechanism using a viscoelastic body is for large-scale buildings, and to apply it for small-scale buildings, such as a wooden house or a light-weight steel-frame house, a convenient mechanism is demanded in consideration of the cost. The present invention offers a vibration damping mechanism which is still more convenient in configuration, and can efficiently reduce the vibration of a structure.
Thin-plate anti-earthquake wall materials are connected to a framework (beam or column) for a building or the like, and when the deformation of the framework is small, the thin plate provides a high rigidity in conjunction with the frame work. However, when the deformation of the framework is great, the thin plate buckles (so-called wrinkles are produced), resulting in the rigidity being reduced. For this reason, such buckling has been considered to be harmful, and for thin-plate buckling phenomena, the buckling deformation and load have been determined with high accuracy, and reasonable reinforcing methods for preventing the buckling have been devised. For example, the shear load bearing material used in an airplane, a vehicle, a ship, a bridge, a building or the like is an aggregate of a thin plate and a number of reinforcing materials, being free from elastic buckling, in other words, being configured so that plastic buckling can be caused, and with the plastic buckling, the distortion energy is absorbed and the vibration is reduced. Consequently, because the buckling load for a shear load bearing material (having a length of the shorter side of "a" and a thickness of "t") is in proportion to (t/a).sup.2, the value of (t/a) is made sufficiently large to prevent buckling from being caused within the limit of elastic deformation.
Therefore, a framework to which an anti-earthquake wall material free from elastic buckling is connected has practically no capacity to absorb the vibration energy, providing a construction which has strength, but rocks significantly in an earthquake or a typhoon. On the other hand, a framework to which an anti-earthquake wall material causing plastic buckling is connected provides an effect of preventing rocking of a building by absorbing the plastic distortion, but brings about a substantial reduction in rigidity, the external force to be born by the anti-earthquake wall material being transferred to the framework connected to the anti-earthquake wall material, which results in an increase in deformation of the framework, leading to plasticization of the framework, and at the subsequent stage, a collapse of the structure. In other words, if an anti-earthquake wall material free from elastic buckling is used, a structure which significantly rocks in an earthquake or a typhoon is provided, and only if the anti-earthquake wall material has been plasticized through a great deformation in an earthquake, is the degree of rocking of with the structure decreased. However, if an anti-earthquake wall material is an elastic body, and yet is provided with an energy absorbing capability, a structure with which the degree of rocking is low, and which will not collapse can be produced. As the energy absorption mechanism, a damper is available, but the damper will not contribute any increase in strength and rigidity. The present invention offers an anti-earthquake wall material which is provided with features of strength, rigidity, and energy absorbing capability.